Thermotropic liquid crystals derived from benzopyranobenzopyran−dione. Preparation and physical characterization

Tetra−, penta− and hexasubstituted benzopyranobenzopyran−dione with side chains linked via ether or ester groups yield highly polymorphic compounds. The penta− and hexasubstituted ether and ester series include homologues which exhibit columnar discotic mesophases. Miscibility experiments on the ether series indicate that their mesophases are of the Dh (DE) class. The tetrasubstituted ethers do not appear to be mesogenic, while the corresponding esters were previously shown to exhibit a highly ordered cubic phase. Differential scanning calorimetry, optical polarizing microscopy and X−ray measurements were used to characterize the mesophases and determine their structural parameter